In general, a voltage step-up circuit generates an output voltage with a desired voltage level by stepping up an input voltage. For example, this type of voltage step-up circuit is a circuit in which diode-connected transistors are serially connected to one another, and a capacitor is connected between each of the transistors, respectively.
According to such a circuit configuration, a voltage is stepped up stepwise in units of the voltage obtained by subtracting a threshold voltage of the transistor from the input voltage. Even if the number of connection steps of the transistor is increased, the threshold voltage of the transistor is subtracted from the input voltage for each of the connection steps. Therefore, in order to obtain the output voltage with a high voltage level, there is a possibility that the number of steps of the voltage step-up circuit may have to be increased by is so much that the internal voltage of the device will exceed a voltage breakdown limit of the voltage step-up circuit. In addition, as the number of the connection steps is increased, the current consumption is increased, thus causing a disadvantage in terms of the power consumption and power efficiency.
It has also been proposed to change the above-described circuit configuration to a voltage step-up circuit system that does not lead to a loss equivalent to the threshold voltage of the transistor with each step. However, although such a voltage step-up circuit in general has an excellent voltage step-up capability, the operation speed may be slow or the power consumption may be even higher.